1. Field of the Invention
The present invention relates to a clutch mechanism in a gear transmission which is used to establish and interrupt the transmission of rotation from an input shaft to an output shaft.
2. Description of the Prior Art
Hitherto, gear transmission apparatus are known in which the transmission of rotation is established and interrupted by a clutch having pawls. An example of such an apparatus will be described with reference to FIGS. 1 and 2.
An electric motor 41 has its rotary shaft extending to the inside of a casing 42 where the rotary shaft serves as an input shaft 43. An externally toothed input gear 44 is fitted on the input shaft 43 and fixed thereto, while it is in meshing engagement with an externally toothed output gear 45, so that the speed of rotation of the input shaft 43 can be changed (reduced or increased). The externally toothed output gear 45 is loosely fitted on an output shaft 46. An annular, stationary clutch component 48 is fixed by means of bolts 47 to one end face of the externally toothed output gear 45. On the other hand, a slidable clutch component 49 is provided in opposition to the stationary clutch component 48. These clutch components 48 and 49 constitute a clutch. The slidable clutch component 49 is arranged through a sliding key 50 fixed to the output shaft 46, in such a manner that the clutch component 49 is axially slidable relative to the output shaft 46 and is prevented from rotating relative thereto. The sliding key 50 is fitted in a keyway 51 formed in the output shaft 46. The sliding clutch component 49 has an engagement groove 52 formed in the outer periphery thereof and engaging with a shifting device, described later. On the end faces of the clutch components 48 and 49 on which they oppose each other, engagement pawls are provided. As shown in FIG. 2, the engagement pawls comprise several circular-arc recesses 53 and projections 54 which are alternately formed around the circumference.
The engagement pawls operate in the following manner.
When the slidable clutch component 49 is slid by the shifting device, the clutch components 48 and 49 have their engagement pawls engaged or disengaged. If the clutch is engaged, this causes the output shaft 46 to rotate integrally with the externally toothed output gear 45. If the clutch is disengaged, the transmission of rotation via the externally toothed output gear 45 to the output shaft 46 is interrupted.
The output shaft 46 and the input shaft 43 are disposed in parallel with each other. Bearings 56 and 57 are interposed between the output shaft 46, on one hand, and the casing 42 or a cover 55, on the other. The output shaft 46 is rotatably supported by these bearings 56 and 57.
The shifting device has the following construction.
A cam shaft 58 is inserted through and fitted to the casing 42. A roller shaft 59 is threaded into that end portion of the cam shaft 58 within the casing 42, in such a manner as to be eccentric with respect to the axial center of the cam shaft 58. A roller 61 is fitted on the roller shaft 59 via a bush 60, while rotatably fitted in the engagement groove 52 of the slidable clutch component 49.
With this construction, therefore, when a rotary grip 62 which is threaded into the vicinity of the extra-casing end of the cam shaft 58 is rotated, the slidable clutch component 49 is slid axially on the output shaft 46.
However, the above-described conventional clutch mechanism encountered various problems such as the following:
Because the numbers of the recesses 53 and the projections 54 forming the engagement pawls are small, the following risk is involved. When the clutch components are to be coupled, if the recesses and the projections of the clutch components 48 and 49 are at certain positions, the projections 53 of one clutch component may abut against those of the other, thus resulting in insecure engagement. In order to avoid this risk, in a conventional clutch mechanism, the output shaft 46 is rotated by a small amount whereby the position of the recesses and the projections is changed in order to achieve meshing engagement. This operation, however, has adversely affected operability.
Further, because the clutch components 48 and 49 are formed with engagement pawls on the respective end faces, this makes it difficult to mass-produce these components, and incurs high production cost.
Still further, the engagement of the conventional clutch mechanism requires two clutch components 48 and 49, and several bolts 47 for fixing the stationary clutch component 48 to the externally toothed output gear 45. As a result, the number of component parts required is large, thereby causing an increase in the production cost, and complicating the entire apparatus.